Pseudomonas fluorescens Migula, ¿control biológico o patógeno?

El objetivo de esta revisión es presentar algunos aspectos de interés sobre la bacteria Pseudomonas  fluorescens Migula, su función como agente de control biológico y su reciente acción como patógeno de los cultivos. Su empleo como control biológico para biorremediación, y recientemente su capacidad para infectar tejido vegetal, la han hecho objeto de múltiples estudios en todo el mundo. En la actualidad, la identificación de especies del género  Pseudomonas se realiza a través de  métodos moleculares, entre los que se encuentran  la comparación de secuencias del 16S ARNr o hibridación ARNr-ADN; no obstante, hasta el momento se considera que el gen rpoB es el más adecuado para estos fines a nivel de especies y subespecies. Esta bacteria se clasifica dentro del grupo de  Bacterias Promotoras del Crecimiento, debido a que controlan patógenos en las plantas, ya sea produciendo sustancias inhibitorias o incrementando la resistencia natural de la planta, o como las Bacterias Biocontroladoras Promotoras del Crecimiento Vegetal (Biocontrol-PGPB), que tienen efectos beneficiosos sobre los cultivos (contribuye a la fijación biológica del nitrógeno, síntesis de fitohormonas, promoción del crecimiento de las raíces), se asocian con  especies de plantas y se encuentran en diversos ecosistemas. A principios del siglo XXI esta bacteria comenzó a informarse como patogénica en diferentes cultivos y países.Palabras clave: Pseudomonas, control biológico, organismos patógenos.Pseudomonas fluorescens, biological control or pathogen?Abstract: The aim of this review was to summarize some aspects of interest of the bacterium Pseudomonas fluorescens Migula, its function as a biological control agent and its recent action as a crop pathogen. Its use as a biological control agent, for bioremeditation, and its recently known capacity of infecting plant tissues, have made them an object of several studies around the world. Identification of Pseudomonas species  is currently performed by using molecular methods such as the comparison of 16S rRNA sequences or the rRNA-DNA hybridization although, until now, the rpoB gene is considered the most suitable for the identification and phylogenetic discrimination at a species and subspecies level. This bacterium is classified within the Plant Growth Promoting Bacteria  for its capacity for controlling plant pathogens  by either producing inhibitory substances or increasing the natural resistance of the plant, or as the Biocontrol Plant Growth Promoting Bacteria (Biocontrol-PGPB), which have beneficial effects on crops by contributing to nitrogen fixation, phytohormone synthesis, and  root growth promotion; they associate with plants species and can be found in different ecosystem. At the beginning of the 21th century, this bacterium started to be reported as pathogenic in different crops and countries.Key words: Pseudomonas, biological control, pathogenic organisms

Genetic Variability and Clustering Patterns of Sugarcane (<i>Saccharum</i> spp.) Germplasms with Respect to Sucrose-Related Traits

Fifty-five sugarcane genotypes from around the world were collected and evaluated for potential use as parental material in the USDA ARS Canal Point (CP) sugarcane breeding program in Florida, USA. The genotypes were planted in a trial with four check cultivars on organic soils with four replications, and data were collected for two years [i.e., plant cane (PC) and first ratoon (FR) crops] to assess sucrose-yield-related traits and the cane-yield-related traits in PC. Using a multivariate analysis, variation was observed in all cane—[i.e., stalk weight, stalk population and cane yield] and sugar-yield-related traits [i.e., Brix, Pol, sucrose content and commercial recoverable sucrose (CRS)]. The mean CRS content was greater in the FR crop than the PC crop. Significant variations were attributed to genotype (G), crop cycles (C) and G × C effects. Variations between crop cycles were highly significant for all sucrose yield components, which could complicate the downstream selection of genotypes for sucrose yield. Based on CRS content, genotypes could be grouped into six distinct clusters. Based on plant cane data, cane yield traits (stalk weight, stalk population and cane yield) were used to estimate the breeding values of parents. Of the 55 genotypes, 8 had significantly greater t-BLUP values for cane yield, along with CP 00-1101. Combined sucrose yield traits, (Brix, Pol and sucrose content) from the two crops were used to estimate the breeding values of parents. Of the 55 genotypes, 10 genotypes had significantly greater t-BLUP values for CRS, along with CP 00-1101, CP 96-1252 and CP 01-2390, and can be considered as elite parents in future breeding efforts. These results provide a foundation for the efficient integration of genetic diversity in developing commercial cultivars, with improved sucrose yields, into the CP sugarcane breeding program